Annemarie, here's a link to some data from the 2004 SABAC, along with an excerpt:
Updated Efficacy and Safety Analyses of 3-weekly Trastuzumab Monotherapy in Women with HER2-positive Metastatic Breast Cancer: Results from Twelve Months of Follow-up to a Phase II Study
http://professional.cancerconsultant....aspx?ID=33962
"...Treatment with trastuzumab given once every 3 weeks appears comparable to results of trastuzuamb given weekly in patients with HER2-positive metastatic breast cancer. Trastuzumab given once every 3 weeks can improve patient convenience, which is an especially relevant way in which to administer trastuzumab in patients receiving this treatment for prolonged periods of time. Perhaps direct comparative trials of the different dosing schedules are necessary to confirm the effectiveness of lesser dosing...."
<3 Lolly